The Chill Blog

Natural Refrigerants – The New Cool. So, what are they?

Natural Refrigerants

In the 1970s, scientists discovered the dangerous impact Chlorofluorocarbons (CFCs) have in the Earth’s atmosphere. CFCs were used as foam blowing agents, refrigerants and solvents. It was found that they destroy the ozone layer, so that aggressive UV-B radiation can reach directly to the Earth’s surface causing genetic damage in the cells of people, plants and animals. The F stands for fluorine. Common F-gases include chlorofluorocarbons (CFC), Hydrochlorofluorocarbons (HCFC) and hydrofluorocarbons (HFC). It is the last of these, HFCs, that are the fastest growing contribution to climate change.

F-gases are mostly used in refrigeration and air conditioning even though there are better alternative technologies on the market. The problems happen when F-gases escape, through leaks, during maintenance, or when an appliance is scrapped at the end of its life. The concentration of HFCs (the newest F-gases) in the atmosphere is growing faster than other greenhouse gases and they are far more powerful. The most recent science shows that if we only focus on reducing CO2 and do nothing about HFCs, they will be responsible for 28-45% of climate change by 2050. Even if we didn’t act on CO2 they would still be responsible for 10-20% of climate change by 2050. The threat of F-gases is real, and the time to act is now.

Therefore, in 1987, an international treaty was concluded at Montreal, Canada (the so called Montreal Protocol on Substances that Deplete the Ozone Layer), to prevent the ozone layer from further destruction and begin the phase-out of the use of CFCs and other Ozone Depleting Substances (ODS) like Hydrochlorofluorocarbons (HCFCs).

Much of the refrigeration and air conditioning equipment in Australia uses fluorocarbon refrigerants to facilitate the heat transfer process. Fluorocarbon refrigerants are synthetic chemicals which usually have a high global warming potential, and some still have the potential to cause damage to the ozone layer as well if released to the atmosphere.

F-gases: A climate culprit

Before HFCs, there were CFCs and HCFCs. CFCs and HCFCs were phased out by the Montreal Protocol because they destroy the ozone layer and expose us to harmful ultraviolet rays. The chemicals industry created HFCs as a supposedly “green” replacement for the banned gases. But in reality HFCs are a very serious, but little-known contributor to global warming. Each molecule of a F-gas actually heats the surface of the earth much more strongly than a molecule of carbon dioxide (CO2). HFC134a is the most widely used, and it is more than a thousand times more potent than carbon dioxide in global warming. Alternatives to these chemicals do exist to help minimise the potential environmental risks. Often referred to as ‘Natural Refrigerants’ because the substances also occur in nature, these alternatives include ammonia, carbon dioxide & hydrocarbons. These substances have been used for many years, however, they are now finding their way into applications where previously fluorocarbons were the preferred option. To prevent their emissions reaching these dangerous levels, we have to phase out all ozone-depleting and climate-harming F-gases.

If appliances using HFC 134a were properly taken care of and disposed of, then HFC 134a would hardly ever be released into atmosphere, and F-gases wouldn’t be a problem. But, industry itself says that 59% of the gas ever produced is already in the atmosphere. Allowing these gases onto the market has been like getting “out of the frying pan and into the fire” in environmental terms.

Problems from both old and new F-gases

CFCs and HCFCs are still present in our atmosphere, even though they have been banned by the Montreal protocol. This is because of their very long lifetimes in the atmosphere. We won’t actually see the ozone layer back to pre-1980 levels until around 2065.

In 2005, all F-gases combined were responsible for 17% of the cumulative human contribution to climate change. Most of that warming came from the ozone-depleting products which will be reduced over the next hundred years.

However, even though the Montreal Protocol is in place, there is still a big risk. With a lack of regulation, the HCFCs being phased out will be replaced by HFCs which really pack a punch to the climate. (The phase-out dates are for 2020 in developed countries and 2030 in developing countries.)

So what are the alternatives? And the so called ‘Natural Refrigerants.’ Let’s take a closer review of three alternatives.

Ammonia

The dominant characteristics of ammonia are probably its smell and its acute toxicity. Despite these defects ammonia has been widely used for well over 100 years and has a good safety record. Indeed ammonia has been in use as a refrigerant since long before the invention of fluorocarbons, in fact it was an Australian inventor James Harrison for his ground breaking refrigeration machine patented in 1856.

Provided ammonia systems are designed, operated and maintained in accordance with national safety standards and codes of practice, they do not present an unacceptable degree of risk. You will be familiar with ammonia’s ingredient in household cleaners, fertilizers and household products and also you will be familiar with its potent smell (as mentioned above and colour).

Potential Applications

In recent years, the focus has broadened to look at other applications that ammonia may be suitable for. For years, ammonia has been the refrigerant of choice in large industrial refrigeration applications (ie processing cooling, cold storage, mining). Chillers for building air conditioning, using ammonia as a refrigerant, have been released to the market in recent years, though only a relatively small number of installations in Europe had been reported.

Safety Issues

While ammonia is a toxic substance, it is also found in a number of substances we regularly come in contact with. A glass of drinking water can contain as much as 1mg of ammonia, 200gm steak as much as 13mg & some food additives can contain as much as 18mg. This demonstrates that the human body can deal with ammonia in small quantities. Generally, any amount in the atmosphere below 20 parts per million (ppm) is regarded as not dangerous. At amounts of up to 53 ppm, ammonia’s characteristic odour will be noticeable.

Ammonia has been in consistent use as a refrigerant since the 1800’s. It can be a very efficient alternative to fluorocarbon refrigerants in a number of applications, and has been the refrigerant for many years. Its environmental properties (zero ODP and zero GWP) are also highly favourable.

Concerns do exist regarding the safe use of ammonia as a result of its toxicity and flammability. Many advances have been made in recent years to minimise these risks, however, including using ammonia in conjunction with other refrigerants in order to reduce and isolate the ammonia charge, and using advanced safety equipment.

Carbon Dioxide

Carbon dioxide (CO2) is present in the bread we eat, the beer we drink & the breath we breathe out. It is present in the atmosphere and is non flammable and non toxic. Carbon dioxide has been used in the refrigeration industry since the 1860’s. The use of carbon dioxide as a refrigerant declined between the 1890’s and 1930s for a number of reasons, including changes in technology and the introduction of fluorocarbon refrigerants, which were billed as ‘safety refrigerants’ at the time.

CO2 lends itself to energy and cost-efficient refrigeration systems. Whilst the detailed technical explanation goes beyond this overview, CO2 has several intrinsic properties that are very favourable, including high density (which results in small suction lines), shallow temperature/pressure curve (which results in small suction line losses) and excellent thermodynamic properties (which results in small heat exchangers and close approach temperatures).

It is generally regarded as a cheap and easily available refrigerant, and many experts also regard it as having a ‘unique’ set of properties which make it an ideal refrigerant. In addition to its basic environmental properties, carbon dioxide is non-toxic. It carries an A1 safety classification (the same as most fluorocarbon refrigerants), indicating that it has low toxicity and is non-flammable.

Carbon dioxide is colourless, odourless and is also heavier than air. When used as a refrigerant, carbon dioxide typically operates at a higher pressure than fluorocarbons and other refrigerants. While this presents some design challenges it can usually be overcome in systems designed specifically to use carbon dioxide – more issues may be encountered if carbon dioxide is to be retrofitted to a system designed for a different, lower pressure refrigerant. Carbon dioxide is compatible with some, but not all, commonly used refrigeration system lubricants.

Potential Applications

Carbon dioxide is already being used as a refrigerant in a number of applications around the world, including truck and bus cooling, car air conditioning, in supermarkets and ice-skating rinks, in industrial freezers and in large cold storage applications. Research has also been carried out on the potential for using carbon dioxide as the refrigerant in heat pumps for air conditioning and water heaters.

The availability of equipment rated for carbon dioxides higher pressure has been an issue in the past, however, the technology is now catching up and many companies offers compressors, evaporators and other equipment suitable for use with carbon dioxide.

While there are relatively few installations of this nature currently in Australia, they are becoming more and more commonplace in Europe where companies such as Nestle, Coca Cola, Unilever & Pepsi Co have embraced its use.

A number of experts believe carbon dioxide systems will become more prevalent in the coming years. This is the opinion offered by one expert, Andy Pearson of Star Refrigeration in the United Kingdom: “I believe that they (carbon dioxide systems) will be cheap and they will very common. We have already seen that the systems installed in all applications show extremely good reliability, and they are also of comparable efficiency to traditional designs. Ongoing research and development will provide further improvements in these areas…carbon dioxide refrigeration systems are here to stay for the foreseeable future.”

In 2000, the International Institute of Refrigeration (IIR) identified carbon dioxide’s high working pressures as the main drawback to its use, stating that appropriate equipment needed to be developed for its use to spread. This has since taken place, and carbon dioxide refrigeration systems are indeed beginning to gain popularity.

As with other refrigerants, all applications need to be considered on their merits by experts. It’s favourable environmental and operational properties make carbon dioxide a competitive option in a number of applications.

Hydrocarbons

Hydrocarbon Refrigerants are flammable but are safe to use if handled correctly. It should be remembered that millions of tonnes of hydrocarbons are used safely every year throughout the world for cooking, heating, powering vehicles, and as aerosol propellants for hairsprays, deodorants, whipped cream and cooking sprays etc. Hydrocarbons are refrigerants that can be used as an alternative to fluorocarbon refrigerants in some refrigeration and air conditioning applications. Along with ammonia & carbon dioxide, hydrocarbons were commonly used as refrigerants before the invention of fluorocarbon refrigerants in the 1930’s.

Interest in hydrocarbon refrigerants has been derived in recent years with discussions on the phase out of ozone depleting refrigerants and high-profile publicity campaigns from organisations such as Green Peace, although they have long been used widely in the oil, gas and petrochemicals industries, particularly in very large refrigeration systems.

Basic Properties

The term ‘hydrocarbon’ encompasses a range of substances. The hydrocarbons most commonly used as refrigerants are ethane (known as R170), propane (R290), butane (R600), Isobutane (R600a) and propylene (R1270).

While each of these substances has a different chemical composition, they all share the same basic environmental properties – an ozone depletion potential (ODP) of zero and a global warming potential (GWP) of 3.

It is these properties that have caused a resurgence of interest in hydrocarbons as refrigerants in recent years, fluorocarbon refrigerants can have global warming potentials as high as 3900, so hydrocarbons would pose a much lesser threat to the environment in the event of a leak.

While the refrigerant designations (the “R” numbers) may not be familiar, many of you will be familiar with the common names of the refrigerants listed above. Hydrocarbons are also used, among other things, as barbeque gas and as LPG in our cars. As most of you will be aware, an important property of all these substances in their other applications is that they are flammable. Hydrocarbons are also flammable, and as a result they carry an A3 safety classification – this means they have a low toxicity, but are in the higher range flammability. This does not stop hydrocarbons being used as refrigerants, however, some precautions need to be taken when they are.

Hydrocarbon refrigerants are fully compatible with nearly all lubricants commonly used in refrigeration and air conditioning systems. One major exception to this rule lubricants containing silicone and silicate (additives which are commonly used as anti-foaming agents) – lubricants containing these substances are not compatible with hydrocarbon refrigerants.

Potential Applications

Hydrocarbon refrigerants can be used either in systems designed specifically for their use, or as a replacement in a system designed for a fluorocarbon refrigerant. If a hydrocarbon refrigerant is to be used in a system designed for a different refrigerant (such as a fluorocarbon), it should be noted that some modifications will probably be required to ensure compatibility and address the issues associated with hydrocarbons flammability. The system manufacturer should be consulted before a hydrocarbon is substituted in an existing piece of equipment. Another issue that needs to be addressed when replacing any refrigerant is its compatibility with the lubricant being used in the system. As mentioned above, lubricants containing silicone and silicate cannot be used with hydrocarbons.

Hydrocarbons are already being used in a number of applications. In Europe, many models of domestic refrigerators are charged with hydrocarbon refrigerant in the factory. It is estimated that there are at least 100,000,000 household refrigerators in use around the world containing hydrocarbon refrigerants.

Hydrocarbon refrigerants have a number of favourable properties, and in the event of a leak they pose a much lower direct threat to the environment than fluorocarbon refrigerants. Care needs to be taken to ensure that the flammability will not pose a safety risk, however, when the appropriate precautions are taken hydrocarbon refrigerants can be used effectively in a range of applications.

If a hydrocarbon is to be used as a replacement in a system that wasn’t originally designed for a flammable refrigerant, the equipment manufacturer should be consulted to ensure that the system will be compatible.

In some applications, a hydrocarbon refrigerant may be more efficient and use less energy than a fluorocarbon. Each case should be assessed on its merits by an expert, however, and emissions from both direct refrigerant emissions and the energy system used should be considered.

Conclusions

Alternative refrigerants and alternative refrigerating systems are unlikely to find great acceptance in the building services industry. The field of application of hydrocarbon refrigerants in fully sealed systems will continue to expand but rate of expansion will be slowed by opposition from vested interests. Use of ammonia will continue, especially for larger industrial systems and for larger air conditioning systems. However, the acute toxicity of ammonia suggests that methods of limiting ammonia charge will be implemented.

After an absence of 50 years, carbon dioxide has returned to the field of refrigeration and its use in increasing rapidly. Carbon dioxide will be used as a low temperature refrigerant in cascade systems, as a volatile secondary refrigerant to avoid the high pumping power associated with the circulation of chilled glycol or chilled water and, possibly as a direct refrigerant though that depends on the production of suitable refrigerating compressors.

Disclaimer: Chill is well aware of the harsh impact of refrigeration operations. We have recently invested in over 100’s of thousands of dollars in state of the art comprehensive insulation panels for the build & installation of our new refrigeration & freezer rooms. How we manage the next stage is reviewing our practices to consider “natural refrigerant alternatives” as the next step, and phasing out HCF. This is a big issue for us, and one that we are taking very seriously as part of our overall Sustainability Action Plan.